In general, a thermoelectric material is a material which is applicable to active cooling and cogeneration by using a Peltier effect and a Seebeck effect. The Peltier effect is a phenomenon that when a DC voltage is applied from the outside, holes of a p-type material and electrons of an n-type material are moved to induce heat generation and heat absorption at both ends of the materials. The Seebeck effect is a phenomenon that when heat is supplied from external heat source, electrons and holes are moved to create a current flow in materials, thereby inducing electricity generation
The active cooling using the thermoelectric material neither generates vibration and noise nor uses a separate condenser and refrigerant while improving thermal stability of an element and having a small volume, and accordingly, it is recognized as an environment-friendly method. The active cooling using the thermoelectric material is usable for a free refrigerant refrigerator, air conditioner, various micro-cooling systems, and the like. In particular, when attaching a thermal element to various memory elements, since it is possible to reduce volume and maintain the element at a uniform and stable temperature, performance of the element may be improved as compared to the existing cooling systems.
Meanwhile, when the thermoelectric material is utilized for thermoelectric power generation using the Seebeck effect, since waste heat is possible to be utilized as an energy source, such that it is applicable to various fields for increasing efficiency of energy such as power of automobile engines, exhaust systems, waste incinerators, steel mill waste heat, and medical devices in a human body using body heat or collecting waste heat.
As a factor for measuring performance of the thermoelectric material, a dimensionless thermoelectric figure of merit (ZT) value is used. In order to increase the ZT value, a material having a high Seebeck coefficient, high electric conductivity, and low thermal conductivity is required.
It is known that when a low-dimensional nanostructure is produced by a method for implementing high ZT value, a Seebeck coefficient is increased by a quantum confinement effect, and when energy barrier is made in a metal or thermoelectric semiconductor at a thickness shorter than a mean free path of electrons and longer than a mean free path of phonon, electricity passes, and heat is blocked, such that the ZT value is increased.
It was experimentally found that at the time of creating a superlattice having a PbSeTe layer on PbTe, and a superlattice having Bi2Te3 layers and Sb2Te3 layers stacked on each other in order to actually realize a phonon glass-electron crystal (PGEC) passing electrons and blocking heat, the ZT values are significantly and largely improved (Nature vol. 413, p. 597, 2001). However, since this superlattice creation needs to artificially use a thin film process, expensive facilities are required, and even though the thin film is sufficiently thickened, a thickness of the thin film is merely hundreds of nm, such that it is not actually usable for thermoelectric power generation and cooling devices.